On the computer your student uses to access the course, open Chrome* (don't use any other browsers), then follow the steps in the image below.
* Before deleting history or restarting, you can try logging in using an Incognito window, which bypasses saved passwords, cookies, and cache. See: How to Open an Incognito Window in Google Chrome
Be sure to restart your computer after deleting it.
*If you don't have Chrome, download it here: Chrome.
Step 7: Restart your computer.
Step 8: Open Chrome, type in dive.unhosting.site, and login.
If you continue to have issues, please send an email to support@diveintomath.com and put in the subject "Urgent! Tech Issue".